In the field of absorbent product technology, many attempts have been made to optimise the absorbent capacity and efficiency of absorbent cores by providing regions of increased or diminished basis weight and density in such cores.
In U.S. Pat. No. 4,935,022 (Lash) an absorbent structure is disclosed which has a lower storage layer and an upper acquisition/distribution layer comprising chemically stiffened cellulose fibers and absorbent gelling material. The upper acquisition/distribution layer is of larger surface area than the underlying storage layer. The lower storage layer is formed of an insert, which is placed relative to the upper acquisition/distribution layer such that about 75% of the absorbent gelling material in the lower layer is found in the front two-thirds section of the absorbent structure, and at least 55% of the total amount of absorbent gelling material is found in the front half section.
In U.S. Pat. No. 4,685,915 (Hasse) an absorbent product is disclosed having a core comprising hydrophilic fibers and absorbent gelling material, the core having an area of higher average density and basis weight than the end portions of the core. The area of higher average density and basis weight is located near the center or the front of the absorbent product.
In U.S. Pat. No. 4,834,735 (Alemany) an absorbent core is disclosed having a storage zone and an acquisition region of lower average density and basis weight than the storage zone. The core comprises a mixture of hydrophilic fibers and absorbent gelling particles. The acquisition region is located towards the front of the absorbent core.
In European Patent No EP-B-0 330 675, it is disclosed to introduce absorbent gelling material into specific locations of a horizontal, or x-y plane of an absorbent core using pulsed powder spray guns.
In International patent applications no's WO 91/11163 and WO 91/11165, a dual layer core is disclosed comprising a lower storage layer and an upper fluid acquisition/distribution layer comprising chemically stiffened cellulose fibers, the upper layer being substantially free of absorbent gelling material. The area of the acquisition/distribution layer is between 25% and 100% of the area of the lower storage layer, and is preferably of elongated shape. For adult incontinence products, the acquisition/distribution layer is generally located in the front two thirds of the absorbent article, relative to the backsheet.
In U.S. Pat. No. 4,411,660 (Dawn), an absorbent article is disclosed in which a layer consisting of absorbent gelling material underlies a fibrous layer. The layer of absorbent gelling material can be in the form of particles, fibers or a film.
In International patent application WO 91/04724, a diaper core is disclosed which linearly tapers from a relatively narrow crotch section to a relatively wide back section.
It has been observed by the applicant that especially in the category of adults suffering from incontinence, there is an increased tendency for leakage of the absorbent products when used in a predominantly lying-down position of the user. The majority of adults suffering from a severe incontinence are elderly women, for which leakage in this position is relatively frequent compared to other users.
It is an object of the present invention to provide an absorbent product which provides reduced leakage when used in a lying down position.
It is another object of the invention to provide an absorbent article that is especially adapted for users ranging from walking infants to adults, when confined to a predominantly lying down position.
It is a further object of the invention to provide such an absorbent article which especially reduces leakage among woman users when confined to a predominantly lying down position.
An absorbent structure according to the invention is characterised in that the weight of the absorbent gelling material located in the back half section of the structure is higher than the weight of the absorbent gelling material located in the front half section of the structure. With "back half section" of the absorbent structure is meant the part of the absorbent structure which in use is intended to contact the genitals and the buttocks of the user and extends generally towards the user's back.
Preferably between 55% and 100% by weight of the absorbent gelling material is located in the back half section. More preferably between 60% and 90% and most preferably between 65% and 80% of the absorbent gelling material is located in the back half section.
By concentrating the absorbent material in the back half section of the absorbent article, urine is prevented from leaking from the product when used in the lying down position. Hence the absorbent structures according to the invention are especially adapted to the specific needs of bedridden people.
In one embodiment of an absorbent structure according to the invention, the absorbent material may comprise, in addition to absorbent gelling material, hydrophilic fibers such as fluff pulp, rayon fibers or modified cellulosic fibers, or may be comprised of a foamed absorbent material as described in U.S. Pat. No. 5,268,224 (Desmarais). Applying more absorbent material of this kind in the back half section of the absorbent structure can result in a so-called profiled core, which is of higher caliper in the back half section than in the front half section. Alternatively, the absorbent structure may be compressed to a uniform caliper, such that the density of the structure is highest in the back half section.
In an alternative embodiment of the absorbent structure according to the invention, the total weight of the absorbent material in the back half section is increased versus the total weight of the absorbent material in the front half section. For instance, the surface area of the layer of absorbent material in the back half section may be larger than the surface area of absorbent material in the front half section at equal basis weights of absorbent material in the front half and back half sections. For instance, the distance between a longitudinal side of the absorbent structure and the longitudinal centerline may substantially monotonically increase when going from the transverse center line to the back transverse side. In this way a large surface area of absorbent material is provided in the back half section which not only provides increased absorbent capacity but also provides improved cushioning and softness to the user.
In a further embodiment of an absorbent structure according to the invention, the amount of absorbent gelling material per unit area, or average basis weight, is higher in the back half section than in the front half section.
The average basis weight of the absorbent gelling material in the front half section and in the back half section is determined by measuring the total weight of absorbent gelling material present in any one section and dividing this weight by the total area in which the absorbent gelling material is located. The weight of the absorbent gelling material is determined by separating the absorbent gelling material from the other absorbent material in any one section. The area where the absorbent gelling material is placed, is measured by applying a colouring agent to the absorbent structure, such as bromocresol. The coloured areas are detected by visual inspection. Alternatively, the absorbent structure may be exposed to x-rays to detect the quantity and location of the absorbent gelling material.
In another embodiment of an absorbent structure according to the invention, the average basis capacity in the back half section is higher than the average basis capacity in the front half section. The average basis capacity is a measure of the amount of liquid that can be absorbed per gram of absorbent material. The average basis capacity will depend on the amount and on the type of absorbent material in the front half section and the back half section. The absorbent material in any one section may comprise for instance absorbent gelling material, fibers, foam, interpartically crosslinked aggregates or any combination thereof. The average basis capacity is measured according to a test method which is based on the official method established by the German "Medizinischer Dienst der Spitzenverbande der Krankenkassen e.V." for reimbursement of incontinence absorbent products. The test method "Prufmethode Nr. 1/93 MDS-HI Teil 1, Bestimmung der Flussigkeitsaufnahme" is described in the detailed description of the invention, below.
In a further embodiment of an absorbent structure according to the invention, an acquisition/distribution layer overlies a lower layer of absorbent material, such that the acquisition/distribution layer is for a larger part located on top of the back half section of the lower layer. When the acquisition/distribution layer is of generally elongated shape, a larger length of this layer extends across the back half section of the underlying layer of absorbent material. When the acquisition/distribution layer is of generally circular shape, or is relatively irregularly formed, a larger surface area of the acquisition/distribution layer extends across the back half section of the underlying layer than across the front half section.
The acquisition/distribution layer comprises fibers which retain their resiliency even when wetted, such that the absorbent capacity of the acquisition/distribution-layer does not decrease upon uptake of consecutive gushes of liquid. This property is expressed by the wet-compressibility of the acquisition/distribution layer of at least 5 cm.sup.3 /g and a drip capacity of at least 10 g/g. Hydrophilic fibers which have this property are found among chemically stiffened cellulosic fibers as described in U.S. Pat. Nos. 4,898,642 (Moore), 4,889,597 (Bourbon), 4,889,596 (Schoggen), 5,160,789 (Barcus), 5,049,235 (Barcus) and 4,822,453 (Dean), or by hydrophilic synthetic fibers, such as polyester fibers. The acquisition-distribution layer may alternatively or additionally comprise various types of bicomponent fibers that are thermally bonded to form an open structure. Such fibers described in EP-A-0 513 148 and U.S. application Ser. No. 08/141,156.
The acquisition/distribution layer serves to rapidly take in large gushes of liquid and to quickly lead these away from the body of the wearer, the acquisition/distribution layer has a relatively low density, for instance between 0.03 and 0.13 g/cm.sup.3. Liquids are only temporarily stored in the acquisition/distribution layer. The acquisition/distribution layer is drained by the underlying storage layer, such that it is rapidly emptied and ready for uptake of further gushes of liquid.
For draining of the acquisition/distribution layer, a layer of absorbent gelling particles may be located directly underneath the acquisition/distribution layer. Preferably this absorbent gelling material is of a high gel strength, such that the particles of absorbent gelling material do not deform to such an extent as to form a gelled mass which is relatively impermeable to liquid. Preferably the absorbent gelling material used directly underneath the acquisition/distribution layer has Gel Layer Permeability (GLP) value of at least 4.times.10.sup.-7 cm.sup.3 /s/g. Absorbent gelling materials of these GLP values, maintain a relatively open structure when wet and maintain good liquid transport properties in the vertical (z-direction) and the horizontal (x-y) direction even when wet.